The maintenance of an effective epithelial barrier, which can minimize the penetration of toxic by-products from the microbial flora into the connective tissue, represents one of the most important mechanisms in the resistance of the host to infection. The importance of this mucosal barrier is clearly demonstrated in the gingival sulcus, where the epithelium may be frequently challenged by dense concentrations of bacterial products, and an increase in epithelial permeability may predispose the host to inflammatory periodontal disease. We have previously observed that the basement membrane represents the rate-limiting barrier to the penetration of non-keratinized mucosal epithelium by bacterial endotoxin; and that certain nutritional deficiencies may significantly increase the permeability of this tissue to endotoxin. The purpose of the proposed investigation is to more clearly define the role of the basement membrane in the mucosal barrier, and to determine the effect of a number of nutrient deficiencies of mucosal barrier function and basement membrane biosynthesis. Epithelial barrier function will be investigated by autoradiographically studying the penetration of tritiated dextran of three molecular weights through mucosal tissues. In addition,the effects of ascorbate, vitamin A, folate, protein/calorie and calorie deficiencies on mucosal permeability and the biosynthesis of basement membrane collagen and glycoprotein will be examined.